Titre traduit

Method of analysis of aerodynamic forces for aeroservoelastic interactions studies on F/A-18 and CL-604 aircraft

Résumé traduit

The aeroservoelasticity concerns the interactions studies between the aerodynamic unsteady forces, the active control systems and the flexible aircraft structure modeled by finite elements. In this thesis, one main aspect of the aeroservoelastic interactions multidisciplinary domain is studied on an F/A-18 and on the CL-604 aircraft built at NASA and at Bombardier Aerospace. This aspect is related to the aircraft unsteady aerodynamics, more precisely is related to the conversion methods of the aerodynamic forces from the frequency into Laplace domain.

The aerodynamic forces are calculated in aeroelasticity by use of the Doublet Lattice Methods in the subsonic regime or by use of the Constant Pressure Methods in the supersonic regime on the F/A-18 and CL-604 by use of STARS (STructural Analysis Routines) software and Nastran. One classical method of conversion of the aerodynamic forces from the frequency domain into Laplace domain for the aeroservoelastic interactions studies is the Least Squares (LS) method. A comparison between the initial aerodynamic forces data in the frequency domain calculated by use of STARS and Nastran and the aerodynamic forces calculated by the LS method is presented in this thesis for the F/A-18 and CL-604 aircraft and for different flight conditions (Mach numbers and altitudes). Following this comparison, the values of aerodynamic forces were found to be very close to their approximations by the LS method. Flutter frequencies and speeds obtained with the LS method were found to be very close to the initially frequencies and speeds in the frequency domain.

A better visualization of flutter modes was realized on the CL-604 aircraft, and was further applied on the F/A -18 aircraft, due to the conception, in this thesis, of a better eigenvalues analysis. This method was very helpful to Bombardier Aerospace in a better identification of flutter modes and will be applied in the design of their future aircraft. In this thesis, we found that care should be given to the reduced frequencies range choice for the aeroservoelastic interactions studies.